1. Field of the Invention
The present invention relates to an information processing apparatus which identifies a category to which input data belongs, a method of controlling the information processing apparatus, and a storage medium and, more particularly, to an information processing apparatus which increases the speed and accuracy of identification processing by dividing dictionary data in accordance with the attributes of data, a method of controlling the information processing apparatus, and a storage medium.
2. Description of the Related Art
There have been proposed techniques which identify to which category registered in advance an object expressed by input data belongs by comparing the input data with data registered in advance. A concrete example of this object identification is personal authentication using image data. This technique identifies a person by using a feature unique to the person, such as the face or fingerprint, and is called face authentication or fingerprint authentication. Categories in personal authentication include names and IDs which can specify individuals. In object identification including personal authentication, it is necessary to register in advance an image of an object to be identified as a registered image, together with a name and ID, before the execution of identification. This registration allows to actually execute identification. When an image of an object to be identified (to be referred to as an “input image” hereinafter) is input, the input image is compared with each of the images registered in advance. If there is a registered image matching the input image, a registered object corresponding to the registered image is output as an identification result. If there is no registered image matching the input image, information indicating the absence of the object is output. In the following description of this specification, to identify the category of an object is to determine an individual difference in object (for example, a difference in person). The term “object detection” is similar to the above term. Assume, however, that this term means to determine and detect individuals as those belonging to the same category without discriminating them (for example, to detect faces from images without discriminating individuals).
An application example of personal authentication is personal authentication for security use in managing entering and leaving a given building. In such personal authentication for security use, several thousand to several ten thousand persons may be registered. An increase in the number of registered images in object identification indicates an increase in the number of times of identification, which requires much time to perform identification processing. This is a serious problem when personal authentication must be completed within a given time.
With regard to the problem that the time required for identification processing increases, Japanese Patent Laid-Open Nos. 2002-163655 and 11-353485 have disclosed authentication techniques which speed up identification processing by limiting registered images to be used for the processing.
The technique disclosed in Japanese Patent Laid-Open No. 2002-163655 automatically collects attributes such as pressing forces concerning fingerprints registered in advance, and stores each registered image in any of plurality of divided dictionaries. Each of the divided dictionaries stores a collection of registered images having the same attribute. When collecting a fingerprint to be identified, this technique simultaneously and automatically collects an attribute such as a pressing force, and performs identification for only registered data included in a dictionary matching the attribute. That is, the technique performs attribute determination with respect to both registered images and an input image, and narrows down registered images as identification processing targets based on the determination result. This eliminates the need to perform identification for all the registered images, and hence can speed up the identification processing.
An advantage of the technique of identifying data having the same attribute by performing attribute determination is that it is possible to improve the identification accuracy. For example, it is difficult to perform identification using a captured face image of a face from the front and a captured face image of a face from the side because of a great difference in look. It is however easier to determine, by comparing face images of faces from the front or of faces from the side with each other, whether the persons are the same person rather than when comparing face images from the front and side with each other. It is therefore possible to improve the accuracy of identification by performing identification using face images of faces from the front or face images of faces from the side upon determining the orientation of each face as an attribute. In addition, using methods suitable for identification for faces from the front and for identification for faces from the side can further improve the identification accuracy.
Assume that in this specification, the determination of an attribute of an object means the determination of a characteristic of an object (for example, sex or age) different from a category difference (for example, a person difference).
According to the technique of narrowing down registered images as identification processing targets based on attribution determination results on registered images and an input image, as disclosed in Japanese Patent Laid-Open No. 2002-163655, an error in an attribute determination result makes it impossible to perform correct identification.
With regard to this problem, the following is an example of handling a male face having an androgynous look which is difficult to perform gender determination in a case in which face authentication is performed upon narrowing down dictionaries as registration processing targets and identification processing targets by automatically performing gender determination.
When registering a face to be registered, gender determination is performed for the face to store the registered image in a dictionary corresponding to males or females. When registering a male face having an androgynous look which is difficult to perform gender determination, it is unknown whether the face is determined as a male face and is correctly registered in a dictionary corresponding to males or the face is wrongly determined as a female face and registered in a wrong dictionary. In addition, when a face to be identified is input, this technique performs gender determination for the face, and identifies the registered images stored in a dictionary corresponding to males or females as identification processing targets. At this time, if a male face which is difficult to perform gender determination is input, it is unknown whether the face is determined as a male face and the corresponding dictionary is identified as the dictionary corresponding to males or the face is wrongly determined as a female face and the corresponding dictionary is wrongly identified as the dictionary corresponding to females. Such an attribution determination error at the time of registration or identification may even lead to inability to collate an input image with registered images of persons corresponding to the input image.
In addition, when a method for identification of male faces and a method for identification of female faces are those suitable for the respective purposes, another problem arises. If a male face having an androgynous look which is difficult to perform gender determination is wrongly determined as a female face and registered in a wrong dictionary, this technique may identify the wrongly determined male face by the method suitable for identification using females. Since the identification method needs to identify data which is not assumed to be identified by the method, sufficient identification accuracy may not be obtained.
In order to avoid this problem, a common identification method can be used instead of using different dictionaries for the respective attributes, register a face image in both dictionaries corresponding to males and females if an attribute determination result is unreliable at the time of registration, and perform identification processing for dictionaries corresponding to males and females if an attribute determination result is unreliable at the time of identification. Such a technique, however, cannot achieve an increase in the speed of identification processing and an improvement in identification accuracy, which are the primary objects of the technique.